US20080212908A1 - Fluid Dynamic Bearing Device - Google Patents

Fluid Dynamic Bearing Device Download PDF

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Publication number: US20080212908A1
Authority: US; United States
Prior art keywords: bearing; electroforming; shaft; bearing device; fluid dynamic
Prior art date: 2005-05-18
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.): Abandoned

Application number

US11/795,410

Other languages

English (en)

Inventor

Natsuhiko Mori

Nobuyoshi Yamashita

Fuminori Satoji

Isao Komori

Toshiyuki Mizutani

Masafumi Okuma

Kenichi Mitani

Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)

NTN Corp

Original Assignee

NTN Corp

Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)

2005-05-18

Filing date

2006-05-15

Publication date

2008-09-04

2005-05-18 Priority claimed from JP2005145517A external-priority patent/JP4987248B2/ja

2005-05-18 Priority claimed from JP2005145373A external-priority patent/JP4896428B2/ja

2005-05-18 Priority claimed from JP2005145506A external-priority patent/JP4896429B2/ja

2005-05-18 Priority claimed from JP2005145370A external-priority patent/JP2006322502A/ja

2005-05-18 Priority claimed from JP2005145362A external-priority patent/JP2006322500A/ja

2005-05-18 Priority claimed from JP2005145521A external-priority patent/JP4896430B2/ja

2006-05-15 Application filed by NTN Corp filed Critical NTN Corp

2008-03-28 Assigned to NTN CORPORATION reassignment NTN CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: MORI, NATSUHIKO, MIZUTANI, TOSHIYUKI, OKUMA, MASAFUMI, KOMORI, ISAO, MITANI, KENICHI, SATOJI, FUMINORI, YAMASHITA, NOBUYOSHI

2008-09-04 Publication of US20080212908A1 publication Critical patent/US20080212908A1/en

Status Abandoned legal-status Critical Current

Images

Classifications

- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C17/00—Sliding-contact bearings for exclusively rotary movement
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/02—Parts of sliding-contact bearings
- F16C33/04—Brasses; Bushes; Linings
- F16C33/06—Sliding surface mainly made of metal
- F16C33/10—Construction relative to lubrication
- F16C33/1025—Construction relative to lubrication with liquid, e.g. oil, as lubricant
- F16C33/106—Details of distribution or circulation inside the bearings, e.g. details of the bearing surfaces to affect flow or pressure of the liquid
- F16C33/107—Grooves for generating pressure
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C17/00—Sliding-contact bearings for exclusively rotary movement
- F16C17/02—Sliding-contact bearings for exclusively rotary movement for radial load only
- F16C17/026—Sliding-contact bearings for exclusively rotary movement for radial load only with helical grooves in the bearing surface to generate hydrodynamic pressure, e.g. herringbone grooves
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C17/00—Sliding-contact bearings for exclusively rotary movement
- F16C17/10—Sliding-contact bearings for exclusively rotary movement for both radial and axial load
- F16C17/102—Sliding-contact bearings for exclusively rotary movement for both radial and axial load with grooves in the bearing surface to generate hydrodynamic pressure
- F16C17/107—Sliding-contact bearings for exclusively rotary movement for both radial and axial load with grooves in the bearing surface to generate hydrodynamic pressure with at least one surface for radial load and at least one surface for axial load
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/02—Parts of sliding-contact bearings
- F16C33/04—Brasses; Bushes; Linings
- F16C33/06—Sliding surface mainly made of metal
- F16C33/14—Special methods of manufacture; Running-in
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2370/00—Apparatus relating to physics, e.g. instruments
- F16C2370/12—Hard disk drives or the like
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/4902—Electromagnet, transformer or inductor
- Y10T29/49021—Magnetic recording reproducing transducer [e.g., tape head, core, etc.]
- Y10T29/49025—Making disc drive
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49636—Process for making bearing or component thereof
- Y10T29/49705—Coating or casting

Definitions

the present invention relates to a bearing device for rotatably supporting a shaft member by a dynamic pressure action of fluid, which is generated in a bearing gap.
This type of the bearing device is called a “fluid dynamic bearing device”, and is suitable for use in a spindle motor mounted in an information apparatus, for example, a magnetic disk device such as an HDD and an FDD, an optical disk device such as a CD-ROM/RAM, or a magneto-optical disk device such as an MD/MO, in a polygon scanner motor mounted in a laser beam printer (LBP) or the like, or in a small motor mounted in an electrical apparatus such as an axial fan.
LBP laser beam printer
a shaft member is supported in a non-contact fashion with a bearing member in a radial direction by a dynamic pressure action of fluid, which is generated in a radial bearing gap.
dynamic pressure grooves arranged, for example, in a herringbone configuration are formed as a dynamic pressure generating portion in a predetermined region of at least any one of an outer circumferential surface of the shaft member and an inner circumferential surface of the bearing member, which is opposite thereto.
a rolling machine having a plurality of protrusions is inserted into the inner circumference of the bearing member, and the rolling machine is then allowed to travel thereinto in an axial direction while being rotated alternately in a clockwise direction and a counter clockwise direction, thereby forming the dynamic pressure grooves in the inner circumference of the bearing member.
variation is prone to occur in a shape of the grooves owing to characteristics of the method, and it is difficult to mass-produce highly accurate grooves stably at low cost.
a fluid dynamic bearing device includes: a bearing member; and a shaft member inserted into an inner circumference of the bearing member, and is characterized in that the bearing member is formed by injection molding in which an electroforming portion is inserted, and any one of an inner circumferential surface of the electroforming portion and an outer circumferential surface of the shaft member, which is opposed to the inner circumferential surface of the electroforming portion is provided with a dynamic pressure generating portion formed thereon.
the electroforming portion is formed by an electroforming process of forming a metal layer by causing metal ions to deposit on a master surface. Such the formation of the metal layer can also be performed by using a method similar to electroless plating, as well as a method similar to electrolytic plating.
a forming portion is formed into a non-perfect circular shape in cross section, which corresponds to a shape of the dynamic pressure generating portion, and in a case of forming the dynamic pressure generating portion on the shaft portion, the forming portion is formed into a perfect circular shape in cross section.
the forming portion of a master shaft is transferred to the electroforming portion with high accuracy, and a surface to which the forming portion is transferred has a surface accuracy following to a surface accuracy of the master shaft. Accordingly, if the surface accuracy of the master shaft (in particular, of the forming portion thereof) is enhanced in advance, the inner circumferential surface of the bearing member can be molded with high accuracy, thus making it possible to set the bearing gap with high accuracy.
the bearing member may be fabricated through the steps of: fabricating a master shaft having a forming portion corresponding to a shape of a dynamic pressure generating portion on an outer circumference of the master shaft (master shaft fabrication step); forming an electroforming portion on the outer circumference of the master shaft including the forming portion (electroforming step); performing injection molding while inserting the electroforming portion after the electroforming portion is formed (molding step); and separating the master shaft and the electroforming portion from each other after the injection molding (separation step).
the master shaft and the electroforming portion are separated from each other.
Such the separation can be performed, for example, by allowing an inner stress in a radial expansion direction, which is accumulated in the electroforming portion as the electroforming process is performed, to be released to make the inner circumference of the electroforming portion be thus expanded in diameter.
a diameter expansion amount of the electroforming portion is insufficient only by an operation described above, the master shaft and the electroforming portion are heated or cooled to give a difference in thermal expansion amount therebetween. Then, it becomes possible to smoothly draw out the master shaft from the inner circumference of the bearing member without damaging the dynamic pressure generating portion formed on the electroforming portion.
the master shaft used at the time of molding the electroforming portion may be directly used, and a separate member from the master shaft may be used as well.
the separated master shaft can be repeatedly used in the electroforming process. Accordingly, a highly accurate bearing member can be mass-produced stably.
the dynamic pressure generating portion As an example of the dynamic pressure generating portion, a plurality of dynamic pressure grooves arranged in a herringbone configuration and the like can be exemplified.
a dynamic pressure groove pattern including the dynamic pressure grooves forms an extremely complicated shape. Even in this case, if a forming portion having a portion corresponding to the dynamic pressure groove pattern is formed in advance on the outer circumference of the master shaft in the master shaft fabrication step, the shape of the forming portion is precisely transferred by the electroforming process. Accordingly, the highly accurate dynamic pressure groove pattern can be formed easily at low cost.
the dynamic pressure generating portion formed on the electroforming portion may be formed, for example, of a plurality of circular arc surfaces as well as the above-mentioned dynamic pressure grooves.
the injection molding is performed while inserting the master shaft which has undergone the electroforming process into a mold (insert molding), thereby integrally molding the bearing member composed of the mold portion and the electroforming portion.
a highly accurate part is integrally molded only by enhancing accuracy of the mold and positioning the electroforming portion with high accuracy. Accordingly, if the electroforming portion and the master shaft are thereafter separated from each other, a resultant molded article can be directly used as the bearing member for the bearing device.
the outer circumferential surface of the electroforming portion is formed to have a rough surface. Accordingly, when the insert molding is performed as described above, the injection molding material enters the outer circumferential surface of the electroforming portion, so an adhesion force there between becomes stronger due to an anchor effect.
a flange on the electroforming portion prior to the molding step.
the flange and the mold portion are prevented from being detached from each other or being rotated with respect to each other after the injection molding. Accordingly, much higher adhesion force can be obtained between the electroforming portion and the mold portion.
the flange also includes the one which extends in an oblique direction from the axis center (refer to FIG. 7 ), as well as the one which extends in a perpendicular direction to the axis center (refer to FIG. 6 ).
the flange of the electroforming portion can be formed by plastically deforming the electroforming portion. For example, if an end surface of the electroforming portion, which is brought into intimate contact with the outer circumference of the master shaft, is pressurized in the axial direction, the end portion of the electroforming portion is plastically deformed to the radial outer side thereof since a portion to be pressurized cannot be deformed to the inner diameter side thereof which is brought into intimate contact with the master shaft. Thus, it becomes possible to easily form the outward flange.
the electroforming portion in the case of molding the electroforming portion by the injection molding, if the electroforming portion is partially deformed plastically by clamping of the metal mold, after the flange is formed, the resin or the metal is injected into a cavity while leaving the electroforming portion in which the flange is formed as it is, thus making it possible to form the bearing by the insert molding.
the bearing at low cost without requiring a special process for forming the flange.
the outer circumferential surface of the plastically deformed flange usually becomes a non-perfect circular shape, it becomes possible to form the flange having the outer circumferential surface with the non-perfect circular shape without particularly adding another step.
a metal material, ceramics, and the like are usable as well as the resin material.
the metal material it is possible to use, for example, injection molding of low melting point metal such as a magnesium alloy, so-called MIM molding for performing the injection molding for metal powder and a binder with each other, followed by degreasing and sintering, and the like.
MIM molding injection molding of low melting point metal such as a magnesium alloy
MIM molding for performing the injection molding for metal powder and a binder with each other
degreasing and sintering and the like.
the ceramics it is possible to use, for example, so-called CIM molding for performing the injection molding for ceramic powder and the binder with each other, followed by degreasing and sintering.
the resin material features are obtained that an obtained article is excellent in moldability and lightweight.
an obtained article is excellent in rigidity, conductivity, and heat resistance. Further, in the case of using the ceramics, features are obtained that an obtained article is more lightweight than the metal material and excellent in rigidity, heat resistance, and so on.
the electroforming portion when the electroforming portion is formed into a cylindrical shape, it is conceived that a residual stress in a diameter expansion direction is applied to an inner composition of the electroforming portion after being formed. Meanwhile, in the case of using the resin as the injection molding material, the cylindrical resin mold portion is going to be shrunk as being solidified. Hence, after the resin molding of the electroforming portion, the outer circumferential surface of the electroforming portion and the inner circumferential surface of the resin mold portion are pressed against each other. In addition, while the inner circumferential surface of the electroforming portion becomes a smooth surface corresponding to the outer circumferential surface of the master shaft, the outer circumferential surface of the electroforming portion becomes a rough surface in general. Accordingly, the resin enters irregularities of the surface of the electroforming portion after the resin molding, and an anchor effect is generated. Owing to composite action of the above, the strong adhesion force between the electroforming portion and the resin mold portion can be obtained.
the resin is used as the injection molding material of the bearing member, and a molding shrinkage of the resin is set within a range of 0.02% to 2.0% inclusive.
a molding shrinkage of the resin is set at 0.02% or more, a shrinkage force caused in the resin mold portion at the time when the molten resin is solidified increases. Accordingly, a required adhesion force can be surely ensured between the electroforming portion and the mold portion.
an upper limit of the molding shrinkage is set at 2.0%, thus making it possible to avoid this type of harmful effect.
the dynamic pressure generating portion has a cross section in a radius direction, in which a radius r 1 of a virtual circle inscribed to the inner circumferential surface of the electroforming portion is larger than a radius r 2 of a virtual circle circumscribed to the outer circumferential surface of the shaft member, and in which a sum of a circularity of the bearing surface of the electroforming portion and a circularity of the outer circumferential surface of the shaft member is 4 ⁇ m or less.
the radius r 1 of the inscribed circle of the bearing surface of the electroforming portion and the radius r 2 of the circumscribed surface of the shaft member are set to r 1 >r 2 , and the minimum clearance between the bearing surface of the bearing member and the outer circumferential surface of the shaft member can be thus ensured, thereby making it possible to avoid contact and sliding between the shaft member and the bearing member when they rotate relatively to each other as much as possible to obtain a stable rotation supporting state. Meanwhile, even when the above-mentioned minimum clearance is ensured, if circularities of the bearing surface of the bearing member and the outer circumferential surface of the shaft member are too high, the bearing gap is uneven in the circumferential direction.
a master used at the time of the electroforming process can be directly used as the shaft member.
the surface shape of the master is transferred precisely in a micron order to the inner circumferential surface of the electroforming portion, which serves as the bearing surface. Accordingly, when the sum of the circularity of the bearing surface of the electroforming portion and the circularity of the outer circumferential surface of the shaft member is defined as described above, the circularity of the outer circumferential surface of the shaft member as the master becomes approximately a half (2 ⁇ m) of the above-mentioned sum. Hence, if the master surface is subjected in advance to a finishing process so that the circularity is the above-mentioned numeric value or less, it becomes possible to stably obtain good rotational accuracy and a long lifetime of the bearing.
a member fabricated separately from the master may also be used as well as the master. Also in this case, if a surface of the member is finished so that the circularity thereof is the above-mentioned numeric value or less, which is half of the above-mentioned sum, good rotational accuracy can be obtained stably.
the radii r 1 and r 2 and the circularities are measured on common cross sections in the radius direction. It is necessary that the cross sections in the radius direction be taken at a few arbitrary spots (desirably, three or more spots at an equal interval) in the axial direction, and that the above-mentioned conditions be satisfied at the respective positions thus extracted.
the “circularity” mentioned here means a difference between radii of two concentric geometric circles in the case where an interval of the two concentric circles becomes the minimum when a circular body is sandwiched by the two concentric geometric circles (refer to FIG. 36 ).
a thrust bearing surface for supporting the end portion of the shaft member in the thrust direction can be formed.
a member (thrust plate and the like) constructing the thrust bearing surface into the main body by means such as press-fitting and adhesion. Accordingly, the number of steps and the number of parts are reduced, thus making it possible to achieve cost reduction of the bearing device.
a dynamic bearing for supporting the shaft member in a non-contact fashion in the thrust direction by a dynamic pressure action of fluid, which is generated in a thrust bearing gap between the thrust bearing surface and an end surface of the shaft member, the end surface being opposite thereto, can also be used as well as a pivot bearing for supporting the shaft member in a contact-fashion in the thrust direction on the thrust bearing surface.
the dynamic bearing can be constructed, for example, by forming a plurality of dynamic pressure grooves on any one of the thrust bearing surface and the end surface of the shaft member, which is opposite thereto.
the dynamic pressure grooves of the thrust bearing surface can be formed by the electroforming process with high accuracy.
the electroforming process is performed by a master shaft in which the shaft end is formed into a flat surface, and the thrust bearing surface is formed into a flat surface shape which does not have the dynamic pressure generating portion. Then, after the electroforming portion and the master shaft are separated from each other, a shaft member in which the dynamic pressure grooves are formed in advance on the end surface in another step is inserted into the inner circumference of the shaft member, and the dynamic bearing is thus constructed.
another thrust bearing surface may also be formed on the other end of the master shaft, as well as the forming portion for forming the thrust bearing surface is formed on one end of the master shaft.
the thrust bearing portion can be constructed between the bearing constructing portion of the master shaft and the thrust bearing surface of the electroforming portion.
the bearing constructing portion of the master shaft for example, there is considered a construction in which the plurality of dynamic pressure grooves are formed on the end surface, a construction in which the end surface is formed into the flat surface, or a construction in which the shaft end is formed into a spherical shape.
the dynamic bearing is composed of the bearing constructing portion of the master shaft and the thrust bearing surface
the pivot bearing is composed of the bearing constructing portion and the thrust bearing surface.
the bearing device having the above-mentioned construction can be preferably used for a motor, for example, a spindle motor for the disk device such as the HDD.
This motor is characterized by being inexpensive, and in addition, in that rotational accuracy and durability are high.
the dynamic pressure generating portion is formed on any one of the inner circumferential surface of the electroforming portion and the outer circumferential surface of the shaft member, which is opposite thereto.
the respective constructions described above can also be applied similarly to the case (perfect circular bearing) where any of the inner circumferential surface of the electroforming portion and the outer circumferential surface of the shaft member, which is opposite thereto, has a perfect circular shape in cross section, which does not have the dynamic pressure generating portion.
the master shaft is formed into the perfect circular shape in cross section.
the radial bearing surface (inner circumferential surface of the electroforming portion) of the bearing member is formed into the perfect circular shape.
the shaft member with the perfect circular shape is inserted into the inner circumference of the bearing member after the master shaft and the electroforming portion are separated from each other, and a radial bearing gap with the perfect circular shape is thus formed between the radial bearing surface with the perfect circular shape and the outer circumferential surface of the shaft member with the perfect circular shape in cross section, which is opposite thereto.
a bearing member having a highly accurate dynamic pressure generating portion can be provided stably at low cost. In addition, powder that may be generated by cutting is not generated when the dynamic pressure grooves are formed, and an occurrence of contamination can be avoided.
the bearing device can exert bearing performance which is stable for a long period of time, and the number of parts and the number of assembly man-hours can be reduced, thus making it possible to achieve cost reduction.
a bearing member 8 having a construction of the present invention which is shown in FIG. 1 , is fabricated through the steps of: fabricating a master shaft (refer to FIG. 2A ); masking a spot of the master shaft 12 , which requires the masking (refer to FIG. 2B ); forming an electroforming shaft 11 by performing an electroforming process for an unmasked portion of the master shaft 12 (refer to FIG. 2C ); forming the bearing member 8 by molding an electroforming portion 10 of the electroforming shaft 11 with a resin and the like (refer to FIG. 5 ); and separating the electroforming portion 10 and the master shaft 12 from each other.
the master shaft 12 shown in FIG. 2A is formed of a conductive metal material, for example, stainless steel subjected to a quenching treatment.
a conductive metal material for example, stainless steel subjected to a quenching treatment.
metal materials other than the stainless steel for example, a nickel alloy, a chromium alloy, and the like can also be used.
Even a nonmetal material such as ceramics can be used as the master shaft by being subjected to a conducting treatment (for example, by forming a conductive metal coating film on a surface thereof). It is desirable that a surface of the master shaft 12 be subjected in advance to a surface treatment for reducing a frictional force between the electroforming portion 10 and itself, for example, to fluorine resin coating.
the master shaft 12 can also be formed of a hollow shaft or a solid shaft formed by filling a hollow portion with a resin.
a forming portion N having an irregular shape corresponding to a shape of radial bearing surfaces A described later is formed. Aspects of irregularities of the forming portion N and the radial bearing surfaces A are completely opposite to each other, and protruding portions of the radial bearing surfaces correspond to recessed portions 12 a 1 and 12 a 2 , of the forming portion N.
the example shown in the figure illustrates the case where the recessed portions 12 a 1 and 12 a 2 are formed into a configuration corresponding to a dynamic pressure groove pattern of a herringbone shape; however, the recessed portions 12 a 1 and 12 a 2 can also be formed into a configuration corresponding to a dynamic pressure groove pattern of a spiral shape.
the forming portion N is formed, for example, by using a surface treatment process such as etching as well as a cutting process and a machining process such as a pressing process.
Accuracy of the outer circumferential surface 12 a of the master shaft 12 including the forming portion N directly affects molding accuracy of a dynamic pressure generating portion, and eventually, bearing performance of a dynamic bearing. Accordingly, it is necessary to increase in advance accuracies in circularity, cylindricality, surface roughness, and the like, which are important for functions of the bearing device.
a masking 13 is applied to the outer circumferential surface 12 a of the master shaft 12 , except for the forming portion N. It is possible to use the existing articles which are non-conductive and have corrosion resistance to an electrolytic solution as a material of the masking 13 .
the electroforming process shown in FIG. 2C is performed in such a manner that the master shaft 12 subjected to the masking process is immersed into an electrolytic solution containing metal ions of Ni, Cu, or the like to cause the target metal to deposit onto the surface of the master shaft 12 by applying power to the electrolytic solution.
a sliding material such as carbon or a stress relaxing material such as saccharin may also be contained according to needs.
a type of such the electro deposited metal is selected as appropriate according to physical properties and chemical properties, such as hardness and fatigue strength, which are required for the dynamic pressure generating portion.
the thickness is optimally set according to required bearing performance, a size of the bearing, and further, to a purpose thereof and the like. For example, in a rotational bearing with a shaft diameter of 1 to 6 mm, it is preferable to set the thickness within a range of 10 to 200 ⁇ m.
the electroforming portion 10 is formed by using the method similar to electrolytic plating. Further, the electroforming portion 10 may also be formed by using a method similar to electroless plating.
the electroforming shaft 11 is formed, in which the cylindrical electroforming portion 10 adheres to the region (forming portion N) of the outer circumferential surface 12 a of the master shaft 12 , which excludes the masking 13 .
the irregular shape of the forming portion N formed on the outer circumferential surface 12 a of the master shaft 12 is transferred, thus forming the plurality of dynamic pressure grooves as the dynamic pressure generating portion.
a coating material 3 for the masking is thin, in some cases, as shown by the broken lines of FIG. 3 , both ends of the electroforming portion 4 protrude to the coating material 3 side, and tapered chamfered portions 4 a are formed on the inner circumferential surface of the electroforming portion.
the electroforming shaft 11 is conveyed, for example, to a molding step shown in FIG. 4 , and injection molding (insert molding) using a resin material is performed by using the electroforming shaft 11 as an insert part.
the electroforming shaft 11 is supplied to a metal mold composed of an upper mold 15 and a lower mold 16 in a state where an axial direction thereof is in parallel with a clamping direction (vertical direction in FIG. 4 ) of the metal mold.
a positioning hole 18 corresponding to an outer diameter dimension of the master shaft 12 is formed.
a lower end of the electroforming shaft 11 conveyed from the previous step is inserted, and positioning is effected for the electroforming shaft 11 .
a lower end surface of the electroforming portion 10 in the electroforming shaft 11 engages with a molding surface of the lower mold 16 , and an upper end of the electroforming portion 10 protrudes from a parting line P.L.
a depth L 3 of the positioning hole 18 is larger than a distance L 4 between a lower end of the master shaft 12 and a lower end of the electroforming portion 10 (L 3 >L 4 ). Hence, in a state before swaging, a lower end surface of the master shaft 12 is floated from a bottom of the positioning hole 18 . By adjusting an amount of the floating, an amount of plastic deformation of a flange formed on the lower end of the electroforming portion 10 can be changed.
a guide hole 19 is formed coaxially with the positioning hole 18 .
a depth L 5 of the guide hole 19 is sufficient if the depth L 5 is to an extent where an upper end of the master shaft 12 does not reach or contact a bottom of the guide hole 19 at a time of swaging shown in FIG. 5 (note that the lower end of the master shaft 12 reaches and contacts the bottom of the positioning hole 18 ).
the lower end portion of the electroforming portion 10 which abuts on the molding surface of the lower mold 16
the upper end portion of the electroforming portion 10 which abuts on the molding surface of the upper mold 15
flanges 20 are formed on both axial ends of the electroforming portion 10 .
the resin material is injected into a cavity 17 through a spool 21 , a runner 22 , and a gate 23 , and the insert molding is performed.
the resin material the one is preferable, which is excellent in mechanical strength as well as oil resistance, heat resistance, and the like. It is possible to use, for example, high performance crystalline polymer such as liquid crystal polymer (LCP), a polyphenylene sulfide (PPS) resin, a polyacetal (POM) resin, and a polyamide (PA) resin as the resin material.
LCP liquid crystal polymer
PPS polyphenylene sulfide
POM polyacetal
PA polyamide
these are mere examples, and it is possible to select resin materials appropriate for the purpose and using environment of the bearing from a variety of the existing resin materials. According to needs, a variety of fillers such as a reinforcement (in any form including fiber and powder) and a lubricant may also be added to the resin material.
the one is selected, in which a molding shrinkage (predicted value after the addition of the filler) is within a range of 0.02% to 2.0% inclusive (preferably, a range of 0.05% to 1.0% inclusive).
a molding shrinkage predicted value after the addition of the filler
the molding shrinkage is less than 0.02%, a sufficient adhesion force cannot be ensured between the electroforming portion 10 and the resin, resulting in anxiety about durability of the bearing.
the molding shrinkage exceeds 2.0%, a shrinking force of the resin portion becomes excessive, which adversely affects the surface accuracy of the bearing.
Metal injection molding includes molten metal injection molding and metal powder injection molding, and either of those can be adopted in the present invention.
the former one is a technology in which metal chips and slugs are molten or semi-molten, then flown into the metal mold, followed by the molding.
low melting point metal such as a magnesium alloy or an aluminum alloy
a melting facility can be downsized.
the latter one is a technology in which metal powder and a binder are mixed/kneaded together and caused to flow into the metal mold to be then taken out from the metal mold, and degreased and sintered. This technology is called metal injection molding (MIM) in general.
MIM metal injection molding
the metal to be used is not limited to the low melting point metal such as the magnesium alloy or the aluminum alloy, and other metal materials such as a copper alloy, an iron alloy, and a copper-iron alloy can be widely selected according to the purpose of the bearing.
the metal is used as an injection molding material, thus making it possible to further-enhance the strength, the heat resistance, the conductivity, and the like as compared with the case of using the resin material.
ceramics can be used. It is possible to use, for example, so-called CIM molding or the like, in which a mixture of ceramic powder and the binder is injection molded, and then is degreased and sintered. In this case, a feature is obtained that the injected material is lighter than the metal material and more excellent than the resin material in rigidity and heat resistance.
the mold is opened. Then, a molded article as shown in FIG. 3 is obtained, in which the electroforming shaft 11 composed of the master shaft 12 and the electroforming portion 10 and a mold portion 14 are integrated together.
the above-mentioned molded article is then conveyed to a separation step, where the molded article is separated into a member (bearing member 8 ) in which the electroforming portion 10 and the mold portion 14 are integrated together and into the master shaft 12 .
the bearing member 8 and the master shaft 12 are separated from each other.
a residual stress accumulated in the electroforming portion 10 is released, an inner circumferential surface 10 a of the electroforming portion 10 is expanded in a radius direction, and a gap (desirably, larger than a depth of the dynamic pressure grooves) is formed between the inner circumferential surface 10 a of the bearing member 8 and the outer circumferential surface 12 a of the master shaft 12 .
a diameter expansion amount of the electroforming portion 10 can be controlled within a range of 1 ⁇ m to several ten ⁇ m, for example, by changing the thickness of the electroforming portion 10 .
the master shaft 12 is formed in advance of the metal material or the ceramic material as described above, deformation of the master shaft 12 can be avoided even under a high-temperature/high-pressure environment at the time of the injection molding. Hence, deformation of the forming portion N at the time of the injection molding can be avoided, and accordingly, the radial bearing surfaces A can be formed with high accuracy. Further, the master shaft 12 separated from the electroforming portion 10 can be repeatedly used for the fabrication of the bearing member 8 , and the radial bearing surfaces A are formed into a shape corresponding to that of the forming portion N of the master shaft 12 . Hence, fabrication cost of the master shaft 12 can be suppressed, and in addition, the bearing member 8 including the dynamic pressure generating portion, in which accuracy is less varied from others and high, can be mass-produced stably.
an outer surface of the electroforming portion 10 is formed into a rough surface owing to characteristics of the electroforming process. Accordingly, at the time of the insert molding, the material constructing the mold portion 14 enters micro irregularities on the outer surface of the electroforming portion, thereby exerting a strong adhesion force due to an anchor effect. Further, as described above, in the present invention, the flanges 20 are formed on the electroforming portion 10 , and the electroforming portion 10 is subjected to the insert molding in a form of including the flanges 20 as well. Accordingly, detachment prevention and rotation prevention are effected between the electroforming portion 10 and the mold portion 14 .
the adhesion force between the electroforming portion 10 and the mold portion 14 increases, thus making it possible to provide the bearing member 8 having excellent durability and high reliability.
a shape of outer circumferential surfaces 20 a of the flanges 20 becomes a non-perfect circular shape having random irregularities.
a high effect of preventing the rotation is obtained.
the irregularities of the outer circumferential surfaces 20 a are drawn in an exaggerated manner for the purpose of facilitating the understanding.
the inner circumferential surface of the electroforming portion 10 randomly shrinks in diameter due to an injection pressure, and there is a risk that an accuracy decrease of the inner circumferential surface 10 a is brought.
the flanges 20 are formed by the plastic deformation; however, the flanges 20 can also be formed by other methods than the plastic deformation.
FIG. 7 if the master shaft 12 is formed in advance into a shaft shape with a step difference, when the master shaft 12 is immersed into the electrolytic solution in the electroforming step, inclined flanges 20 as shown in FIG. 7 can be formed on corner portions 12 a of the master shaft 12 after the end of the electroforming depending on electroforming conditions. This is because, in general, a deposition amount of metal particles increases in the corner portions 12 a as compared with that in other smooth portions of the master shaft 12 .
the electroforming portion 10 including the flanges 20 is formed by the injection molding (as shown by a chain double-dashed line) after the formation of the flanges 20 , the effect to prevent the electroforming portion 10 from being peeled off or being rotated can be obtained similarly to the above.
the two radial bearing surfaces A composed of a plurality of dynamic pressure grooves 8 a 1 and 8 a 2 and the protruding portions for defining the dynamic pressure grooves 8 a 1 and 8 a 2 are formed vertically apart from each other.
the radial bearing surfaces A form a radial bearing gap with an outer circumferential surface of a shaft member 2 as the bearing member 8 is incorporated into the bearing device.
the fluid dynamic bearing device 1 includes in addition to the bearing member 8 , as main constituent parts, a housing 7 which has a bottom portion 7 c on one end thereof, for fixing the bearing member 8 to an inner circumference thereof, the shaft member 2 inserted into the inner circumference of the bearing member 8 , and a seal member 9 .
a housing 7 which has a bottom portion 7 c on one end thereof, for fixing the bearing member 8 to an inner circumference thereof, the shaft member 2 inserted into the inner circumference of the bearing member 8 , and a seal member 9 .
the seal member 9 side is an upper side and an axially opposite side to the seal member 9 side is a lower side for the sake of convenience of the description.
the housing 7 is formed into a closed-end cylindrical shape formed of a metal material such as stainless steel or brass or a resin material.
the housing 7 includes an opening portion 7 a at one end, and the other end thereof is sealed.
the housing 7 further includes a cylindrical side portion 7 b , and the bottom portion 7 c on the opposite end side of the side portion 7 b with respect to the opening portion 7 a .
the side portion 7 b and the bottom portion 7 c are formed separately from each other, and the bottom portion 7 c is fixed to a lower inner circumference of the side portion 7 b by means such as adhesion, press-fitting, and welding.
a plurality of dynamic pressure grooves for example, arranged in a spiral configuration or a herringbone configuration are formed as a dynamic pressure generating portion.
This type of dynamic pressure grooves can be molded through a pressing process and the like simultaneously with the molding of the bottom portion 7 c .
the side portion 7 b and the bottom portion 7 c can also be formed integrally. Note that the materials for forming the side portion 7 b and the bottom portion 7 c may be either the same or different from each other as long as the materials can meet performance required therefor.
the shaft member 2 is formed, for example, of a metal material such as stainless steel separately from the above-mentioned master shaft 12 .
the shaft member is composed of a shaft portion 2 a , and a flange portion 2 b provided on one end of the shaft portion 2 a integrally or separately.
An outer circumferential surface of the shaft portion 2 a forms a perfect circle in cross section, which does not have the dynamic pressure grooves or the like.
the shaft member 2 can also be formed into a hybrid structure composed of a metal portion and a resin portion, as well as is formed only of the metal material (for example, the shaft portion 2 a is formed of a metal material, and the flange portion 2 b is formed of a resin material).
An outer diameter dimension of the shaft portion 2 a is slightly smaller than an inner diameter dimension of the protruding portions, which define and form the dynamic pressure grooves 8 a 1 and 8 a 2 , in the radial bearing surfaces A formed on the bearing member 8 .
the radial bearing gap approximately in a range of 1 ⁇ m to several ten ⁇ m is formed between the outer circumferential surface of the shaft portion 2 a and the two radial bearing surfaces A.
the seal member 9 formed of a metal material such as brass or a resin material is fixed by means such as the press-fitting and the adhesion.
the seal member 9 forms an annular shape, and is formed separately from the housing 7 .
An inner circumferential surface 9 a of the seal member 9 is opposite to the outer; circumferential surface of the shaft portion 2 a through a seal space S having a predetermined volume.
the outer circumferential surface of the shaft portion 2 a which is opposite to the seal space S, is formed as a tapered surface 2 a 2 gradually reduced in diameter as extending upward, and also functions as a centrifugal seal when the shaft member 2 is rotated.
an inner space of the fluid dynamic bearing device 1 hermetically sealed by the seal member 9 is filled with, for example, lubricating oil as lubricating fluid, and in this state, an oil level of the lubricating oil is maintained within the seal space S.
the seal member 9 can also be formed integrally with the housing 7 for the purpose of reducing the number of parts and the number of assembly man-hours.
the bearing member 8 is fixed to an inner circumferential surface of the side portion 7 b of the housing 7 .
fixing means such as the press-fitting, the adhesion, a combination thereof, and the welding is selected according to design conditions.
the shaft member 2 is rotatably inserted into the inner circumference of the bearing member 8 .
the bearing member 8 has a composite structure composed of the mold portion 14 formed of the resin material, and the electroforming portion 10 fixed and attached to the inner circumferential surface of the mold portion 14 , and the bearing 8 is formed into the cylindrical shape.
the mold portion 14 and the electroforming portion 10 are fixed and attached to each other with a strong force over the overall lengths in the axial direction, and the flanges 20 extending in the diameter direction are formed on the upper and lower end portions of the electroforming portion 10 , thus detachment prevention and rotation prevention are effected between the mold portion 14 and the electroforming portion 10 .
the herringbone-shaped dynamic pressure grooves 8 a 1 and 8 a 2 are individually formed on the radial bearing surfaces A of the inner circumferential surface 8 a of the bearing member 8 by the above-mentioned electroforming process.
the dynamic pressure groove 8 a 1 in the upper region is formed asymmetrically in the axial direction with respect to an axial center m (axial center of a region across upper and lower inclined grooves), and an axial dimension X 1 of an upper region of the dynamic pressure groove 8 a 1 from the axial center m is larger than an axial dimension X 2 of a lower region thereof. Therefore, feeding force (pumping force) of the lubricating oil by the dynamic pressure grooves when the shaft member 2 is rotated is relatively larger in the upper dynamic pressure groove 8 a 1 than in the lower symmetric dynamic pressure groove 8 a 2 .
a plurality of dynamic pressure grooves arrayed, for example, in a spiral shape are formed as dynamic pressure generating portions.
This type of dynamic pressure grooves can be molded simultaneously with the forming of the bearing member 8 as long as a groove shape is formed in advance on a region of the lower mold 16 , which is opposite to the lower end surface 8 c .
the lower mold 16 is the one to be used in the molding step of forming the above-mentioned bearing member 8 .
the fluid dynamic bearing device 1 is constructed as described above, and when the shaft member 2 is rotated, the two upper and lower regions of the inner circumferential surface 8 a of the bearing member 8 , which serve as the radial bearing surfaces A, are individually opposite to an outer circumferential surface 2 a 1 of the shaft portion 2 a through the radial bearing gap. Then, as the shaft member 2 is rotated, dynamic pressure of the lubricating oil is generated in the above-mentioned radial bearing gap, and by the pressure, the shaft portion 2 a of the shaft member 2 is supported in a non-contact fashion with the bearing member 8 rotatably in the radial direction. Thus, a first radial bearing portion R 1 and a second radial bearing portion R 2 , which support the bearing member 2 rotatably in the radial direction in a non-contact fashion therewith, are formed.
the region of the lower end surface 8 c of the bearing member 8 which serves as the thrust bearing surface, is opposite to an upper end surface 2 b 1 of the flange portion 2 b through the thrust bearing gap, and a region of an upper end surface 7 c 1 of the bottom portion 7 c , which serves as the thrust bearing surface, is opposite to a lower end surface 2 b 2 of the flange portion 2 b through the thrust bearing gap.
circulation paths 8 d 1 and 9 b 1 which allow the thrust bearing gaps (in particular, the thrust bearing gap of the first thrust bearing portion T 1 ) and the seal space S to communicate with each other are provided on an outer circumferential surface 8 d of the bearing member 8 and a lower end surface 9 b of the seal member 9 , respectively. Then, the lubricating oil flows between the thrust bearing gaps and the seal space S through the circulation paths 8 d 1 and 9 b 1 , and the pressure difference is released early, and such harmful effects as described above can be prevented. As an example, FIG.
the circulation path 8 d 1 is formed on the outer circumferential surface 8 d of the bearing member 8
the circulation path 8 d 1 can also be formed on the inner circumferential surface of the housing 7
the circulation path 9 b 1 can also be formed on the upper end surface 8 b of the bearing member 8 .
FIG. 10 shows a construction example of a spindle motor for an information apparatus, into which the fluid dynamic bearing device 1 shown in FIG. 9 is incorporated.
the spindle motor is the one to be used for a disk drive device such as an HDD, and includes the fluid dynamic bearing device 1 for rotatably supporting the shaft member 2 in a non-contact fashion, a rotor (disk hub) 3 attached to the shaft member 2 , and a stator coil 4 and a rotor magnet 5 , both of which are opposed to each other through a radial gap.
the stator coil 4 is attached to an outer circumference of a bracket 6
the rotor magnet 5 is attached to an inner circumference of the disk hub 3 .
the housing 7 of the fluid dynamic bearing device 1 is attached to an inner circumference of the bracket 6 .
the disk hub 3 On the disk hub 3 , one or a plurality of disks D such as magnetic disks are held.
the stator coil 4 When the stator coil 4 is energized, the rotor magnet 5 is rotated by an electromagnetic force between the stator coil 4 and the rotor magnet 5 , and the disk hub 3 and the shaft member 2 are thereby rotated integrally with each other.
FIG. 11 shows a construction example of a fluid dynamic bearing device, and further, a motor, using the bearing member 8 of the embodiment shown in FIG. 6 .
the motor has a radial bearing portion R for supporting the shaft member rotatably in the radial direction, and a thrust bearing portion T for supporting the shaft member rotatably in the thrust direction.
the radial bearing portion R is constructed by inserting the shaft member 2 into the inner circumference of the bearing member 8
the thrust bearing portion T is constructed by supporting a convex spherical shaft end of the shaft member 2 by a thrust plate 24 opposed to an end surface of the bearing member 8 in a contact fashion therewith.
the disk drive device such as the HDD
the disks D are charged with static electricity by friction with the air, and the charged static electricity is discharged instantaneously to peripheral devices such as a magnetic head, thus adversely affecting the peripheral devices.
the thrust plate 23 is made of the resin, or when the thrust bearing portion T is composed of the dynamic bearing, a tendency to bring such the adverse effect becomes significant.
the mold portion 14 is formed by the injection molding of the metal material, the static electricity built up on the disks D is discharged rapidly to a ground side through a route of the shaft member 2 ⁇ the electroforming portion 4 ⁇ the mold portion 14 ⁇ a bracket 27 .
the disks D can be restricted from being charged with the static electricity, and a spark can be prevented from occurring between the disks and the peripheral devices.
the above mentioned bearing member 8 can be used not only for the fluid dynamic bearing device 1 shown in FIG. 9 but also widely for fluid dynamic bearing devices with other constructions. A description will be made below of the other constructions of the fluid dynamic bearing device with reference to the drawings. Common reference symbols will be assigned to members having the same constructions as and common functions to those of the fluid dynamic bearing device 1 shown in FIG. 9 , and a repeated description will be omitted.
a fluid dynamic bearing device shown in FIG. 12 is the one, in which the thrust bearing portion T is disposed on the opening portion 7 a side of the housing 7 , and supports the shaft member 2 in a non-contact fashion with the bearing member 8 in one thrust direction.
the flange portion 2 b is provided above the lower end of the shaft member 2 , and the thrust bearing gap of the thrust bearing portion T is formed between a lower end surface 2 b 2 of the flange portion 2 b and the upper end surface 8 b of the bearing member 8 .
the seal member 9 is attached to an inner circumference of the opening portion of the housing 7 , and the seal space S is formed between the inner circumferential surface 9 a of the seal member 9 and the outer circumferential surface of the shaft portion 2 a of the shaft member 2 .
the lower end surface 9 b of the seal member 9 is opposite to the upper end surface 2 b 1 of the flange portion 2 b through an intermediation of an axial gap.
FIG. 13 is a view showing another embodiment of the fluid dynamic bearing device 1 .
the fluid dynamic bearing device 1 shown in FIG. 13 is different from the fluid dynamic bearing device 1 shown in FIG. 9 mainly in the following points.
the seal space S is formed on an outer diameter portion of the housing 7
the thrust bearing portion T 2 is formed between the upper end surface of the housing 7 and a lower end surface 3 a 1 of a plate portion 3 a constructing the disk hub 3 .
FIG. 15 is a view showing still another embodiment of the fluid dynamic bearing device 1 .
This embodiment is largely different from the embodiment shown in FIG. 9 in that a bearing member 28 is formed integrally with the housing 7 in a form of including the housing 7 .
the bearing member 28 is also composed of the mold portion 14 formed of the resin material (metal material in some cases), and the electroforming portion 10 fixed and attached to the inner circumferential surface of the mold portion 14 .
the bearing member 28 is composed of a sleeve-like sleeve portion 28 a capable of inserting the shaft portion 2 a into an inner circumference thereof, a seal fixing portion 28 b extending upward from an outer diameter side of the sleeve portion 28 a and capable of fixing the seal member 9 to an inner circumference of the fixing portion 28 b itself, and a bottom fixing portion 28 c extending downward from the outer diameter side of the sleeve portion 28 a and capable of fixing the bottom portion 7 c to an inner circumference of the bottom fixing portion 28 c itself.
an axial circulation path 29 for allowing an upper end surface 28 a 2 and a lower end surface 28 a 3 thereof to communicate with each other, is provided.
the bearing member 28 is molded while including a portion serving as the housing in the molding step shown in FIG. 4 . Accordingly, the number of parts and the number of assembly man-hours are reduced, thus making it possible to achieve cost reduction of the fluid dynamic bearing device 1 .
FIG. 16 is a view showing yet another embodiment of the fluid dynamic bearing device 1 .
This embodiment is largely different from the embodiment shown in FIG. 13 in that, as in the embodiment shown in FIG. 15 , the bearing member 28 is formed integrally with the housing 7 in a form of including the housing 7 which is a separate body in FIG. 13 . Also in this embodiment, the number of parts and the number of assembly man-hours are reduced, thus making it possible to achieve the cost reduction of the fluid dynamic bearing device 1 .
the above description shows the constructions with which the fluid dynamic pressure is generated by using the herringbone-shaped and the spiral-shaped dynamic pressure grooves.
the present invention is not limited to this.
so-called multi-lobe bearing and step bearing may also be employed as the radial bearing portions R 1 and R 2 .
a plurality of circular arc surfaces (in the multi-lobe bearing) and a plurality of axial grooves (in the step bearing) serve as the dynamic pressure generating portions for generating the dynamic pressures in the radial bearing gaps.
Those dynamic pressure generating portions are formed on the electroforming portion 10 of the bearing member 8 , and a forming method thereof conforms to the respective steps (refer to FIGS. 2A to 2C and 5 ) in the case of forming the dynamic pressure grooves. Accordingly, a description thereof will be omitted.
FIG. 17 shows an example of the case where one or both of the radial bearing portions R 1 and R 2 are composed of the multi-lobe bearings.
the region of the inner circumferential surface 8 a of the bearing member 8 which serves as the radial bearing surfaces, is composed of three circular arc surfaces 33 (this is a so-called three-lobe bearing). Centers of curvatures of the three circular arc surfaces 33 are individually offset by equal distances from a shaft center O of the bearing member 8 (bearing portion 2 a ).
the radial bearing gaps are wedge-like gaps 35 each of which is reduced gradually into wedge shapes in both circumferential directions.
FIG. 18 shows another example of the case where one or both of the radial bearing portions R 1 and R 2 are composed of the multi-lobe bearings.
a region of the inner circumferential surface 8 a of the bearing member 8 which serves as the radial bearing surfaces A, is composed of the three circular arc surfaces 33 (this is the so-called three-lobe bearing).
the radial bearing gaps are wedge-like gaps 35 each of which is reduced gradually into wedge shapes in one circumferential direction.
the multi-lobe bearing with such the construction is sometimes called a tapered bearing.
deeper axial grooves called separating grooves 34 are formed on boundary portions between the three circular arc surfaces 33 .
FIG. 19 shows still another example of the case where one or both of the radial bearing portions R 1 and R 2 are composed of the multi-lobe bearings.
each of predetermined regions 9 on the minimum gap side of the three circular arc surface 33 is composed of a circular arc concentric with the bearing member 8 (shaft portion 2 a ) by taking the shaft center O thereof as the center of curvature.
the radial bearing gap minimum bearing gap
the multi-lobe bearing with such the construction is sometimes called a taper flat bearing.
FIG. 20 shows an example of a case where one or both of the radial bearing portions R 1 and R 2 are composed of the step bearings.
a plurality of axial groove-shaped dynamic pressure grooves 36 are provided at a predetermined interval in the circumferential direction.
the multi-lobe bearings in the above-mentioned respective examples are the so-called three-lobe bearings.
a so-called four-lobe bearing, five-lobe bearing, and a multi-lobe bearing composed of circular arc surfaces of which circular arcs are six or more may also be employed.
the radial bearing portion is composed of the step bearing or the multi-lobe bearing, it is possible to adopt a construction in which a single radial bearing portion is provided over the upper and lower regions of the inner circumferential surface 8 a of the bearing member 8 , as well as a construction in which the two radial bearing portions are provided axially apart from each other like the radial bearing portions R 1 and R 2 .
Those dynamic pressure generating portions are formed of the electroforming portion 10 of the bearing member 8 , and a forming method thereof conforms to the respective steps (refer to FIGS. 2A to 2C ) in the case of forming the dynamic pressure grooves. Accordingly, a description thereof will be omitted.
the thrust bearing portion can also be composed of a so-called step bearing in which a plurality of dynamic pressure grooves with a radial groove shape are provided in the region serving as the thrust bearing surface, of a so-called wave-shaped bearing (in which the step shape turns to a wave shape), and the like (not shown).
the fluid dynamic bearing device 1 is composed of the dynamic bearing which supports the shaft member 2 in a non-contact fashion therewith in the thrust direction.
the fluid dynamic bearing device 1 shown in FIG. 14 is composed of a pivot bearing which supports the shaft member 2 in a contact-fashion therewith in the thrust direction.
a lower end 2 a 3 of the shaft portion 2 a of the shaft member 2 is formed into a convex spherical shape, and the lower end 2 a 3 is supported in a contact fashion by an upper end surface 24 a of the thrust plate 24 fixed to the upper end surface 7 c 1 of the bottom portion 7 c of the housing 7 by means such as adhesion.
a bearing member 8 having a construction of the present invention which is shown in FIG. 21 , is fabricated through a step of fabricating a master shaft 12 (refer to FIG. 22A ), a step of masking a spot of the master shaft 12 , which requires the masking (refer to FIG. 22B ), a step of forming an electroforming shaft 11 by performing the electroforming process for an unmasked portion N of the master shaft 12 (refer to FIG. 22C ), a step of forming a bearing member 8 by molding an electroforming portion 10 of the electroforming shaft 11 with a resin and the like (refer to FIG. 25 ), and a step of separating the electroforming portion 10 and the master shaft 12 from each other.
FIGS. 22A to 22C are basically common to the steps shown in FIGS. 2A to 2C , and accordingly, common matters will be omitted below, and a description will be mainly made below of different matters.
the masking 13 (shown by a scatter pattern) is applied to an upper portion of an outer circumferential surface of the master shaft 12 and to an upper end surface thereof.
electroforming metal is not electrolytically deposited at the time of an electroforming process to be described later, and the electroforming portion 10 is not formed.
the masking is not applied to the outer circumferential surface and lower end surface of the master shaft 12 , except for the masked portion M, and such the portions (unmasked portion N) which are not subjected to the masking become forming portions for forming an inner circumferential surface (radial bearing surfaces A) of the electroforming portion 10 and an inner bottom surface (thrust bearing surface B) thereof at the time of the electroforming process.
a radial bearing surface forming portion N 1 having an irregular shape corresponding to a dynamic pressure groove pattern of the radial bearing surfaces A is formed on the outer circumferential surface of the master shaft 12 . Aspects of irregularities of the radial bearing surfaces A and the radial bearing surface forming portion N 1 are completely opposite to each other, and protruding portions of the radial bearing surfaces A correspond to recessed portions 12 a 1 and 12 a 2 of the radial bearing surface forming portion N 1 .
the shown example illustrates the case where the recessed portions 12 a 1 and 12 a 2 of the radial bearing surface forming portion N 1 correspond to the herringbone-shaped dynamic pressure groove pattern.
the recessed portions 12 a 1 and 12 a 2 can also be formed into a shape corresponding to the spiral-shaped dynamic pressure groove pattern.
a thrust bearing surface forming portion N 2 having an irregular shape corresponding to a dynamic pressure groove pattern of the thrust bearing surface B to be described later is formed. Also on the thrust bearing surface forming portion N 2 , an aspect of irregularities thereof is completely opposite to that of the thrust bearing surface B.
the shown example illustrates the case where the thrust bearing surface forming portion N 2 corresponds to a spiral-shaped dynamic pressure groove pattern.
the thrust bearing surface forming portion N 2 can also be formed into a shape corresponding to a pattern of a herringbone-shaped dynamic pressure groove.
the electroforming shaft 11 is formed, in which the closed-end cylindrical electroforming portion 10 is coated on the unmasked region N of the outer circumferential surface 12 a and lower end surface 12 c of the master shaft 12 .
the electroforming shaft 11 is formed, in which the closed-end cylindrical electroforming portion 10 is coated on the unmasked region N of the outer circumferential surface 12 a and lower end surface 12 c of the master shaft 12 .
a shape of the radial bearing surface forming portion N 1 of the outer circumferential surface 12 a of the master shaft 12 is transferred, and the radial bearing surfaces A having a plurality of dynamic pressure grooves 8 a 1 and 8 a 2 are formed apart from each other in the axial direction.
a shape of the thrust bearing surface forming portion N 2 of the lower end surface 12 c of the master shaft 12 is transferred, and the thrust bearing surface B having the plurality of dynamic pressure grooves is formed (not shown).
the electroforming portion 11 is conveyed to a molding step shown in FIG. 25 , and injection molding (insert molding) using a resin material is performed while taking the electroforming shaft 11 as an insert part.
a molded article is obtained, in which the electroforming shaft 11 , composed of the master shaft 12 and the electroforming portion 10 , and a mold portion 14 are integrated together.
the above-mentioned molded article is then conveyed to a separation step, where the molded article is separated into the one (bearing member 8 ), in which the electroforming portion 10 and the mold portion 14 are integrated together, and the master shaft 12 .
the bearing member 8 separated from the master shaft 12 forms a closed-end cylindrical shape having a side portion 8 b and a bottom portion 8 c which are integral with the bearing member 8 .
an upper end of the electroforming portion 10 is also covered with the mold portion 14 . Accordingly, the electroforming portion 10 can be prevented from being drawn out therefrom.
An inner circumferential surface of such the coating portion of the mold portion 14 is formed as a tapered surface 14 a , and a seal space is formed between the tapered surface 14 a and the outer circumferential surface of the shaft member 2 after the bearing device is assembled as will be described later.
a shaft member 2 fabricated separately from the master shaft 12 is inserted, and a fluid dynamic bearing device (fluid dynamic bearing device) 1 is thus constructed.
the shaft member 2 is formed of a metal material rich in abrasion resistance such as stainless steel, an outer circumferential surface 2 a thereof is formed into a perfect circular shape which does not have the dynamic pressure grooves, and a lower end surface 2 b thereof is formed into a flat surface shape which does not have the dynamic pressure grooves.
An outer diameter dimension of the shaft member 2 is slightly smaller than an inner diameter dimension of regions of the radial bearing surfaces A between the dynamic pressure grooves, which are the protruding portions which define the dynamic pressure grooves.
a radial bearing gap (not shown) approximately in a range of 1 ⁇ m to several ten ⁇ m is formed between the outer circumferential surface of the shaft member 2 and the two radial bearing surfaces A.
the tapered seal space S is formed between the tapered surface 14 a of an upper end opening portion of the mold portion 14 and the outer circumferential surface 2 a of the shaft member 2 .
an inner space of the fluid dynamic bearing device 1 hermetically sealed at the seal space S is filled with, for example, the lubricating oil as the lubricating fluid.
the seal space S can be formed into a cylindrical space having the same width overall, as well as is formed into the tapered space in which an upper space is expanded.
the tapered surface 14 a constructing the seal can also be composed of a separate member from the mold portion 14 .
the fluid dynamic bearing device 1 is constructed as described above.
the dynamic pressure of the lubricating oil is generated in the above-mentioned radial bearing gap, and by the pressure thereof, the shaft member 2 is supported rotatably in the radial direction in a non-contact fashion with the bearing member 8 .
a first radial bearing portion R 1 and a second radial bearing portion R 2 for supporting the bearing member 2 rotatably in the radial direction in a non-contact fashion therewith, are formed.
the thrust bearing surface B of the bearing member 8 is opposite to the lower end surface 2 b of the shaft member 2 through a thrust bearing gap.
the dynamic pressure of the lubricating oil is also generated in the thrust bearing gap, and by the pressure thereof, the shaft member 2 is supported in a non-contact fashion with the bearing member 8 rotatably in the thrust direction.
a thrust bearing portion T is formed, for supporting the shaft member 2 in the non-contact fashion rotatably in the thrust direction.
both of the radial bearing surfaces A and the thrust bearing surface B are formed on the electroforming portion 10 , and the bearing member 8 is formed by the injection molding in which each electroforming portion 10 is inserted. Therefore, the constructions of the radial bearing portions R 1 and R 2 and the thrust bearing portion T can be simplified, and in addition, the number of parts and the number of man-hours can be reduced, thus making it possible to achieve the cost reduction of the bearing device 1 . Further, since the radial bearing surfaces A and the thrust bearing surface B are subjected to the electroforming process, the dynamic pressure grooves with high accuracy can be formed, and high bearing performance can be obtained. In addition, powder that may be generated by cutting is not generated as the bearing surfaces A and B are being molded, and a problem of contamination is also solved.
the master shaft 12 fabricated once can be repeatedly used, and the radial bearing surfaces A and the thrust bearing surface B after being molded are formed into shapes corresponding to the surface shapes of the forming portions N 1 and N 2 of the master shaft.
the bearing member 8 having little variations in accuracies of the dynamic pressure grooves among each other can be obtained, thus making it possible to stably mass-produce the fluid dynamic bearing device 1 having high rotational accuracy.
an outer surface of the electroforming portion 10 is formed into a rough surface owing to characteristics of the electroforming process. Accordingly, at the time of the insert molding, the resin material constructing the mold portion 14 enters into spaces caused by micro irregularities on the outer surface of the electroforming portion 10 , and exerts an anchor effect. Therefore, a strong adhesion force is exerted between the electroforming portion 10 and the mold portion 14 , and the electroforming portion 10 and the mold portion 14 are reliably prevented from being rotated with respect to each other and detached from each other. Hence, it becomes possible to provide the strong bearing member 8 rich in impact resistance.
a flange 20 is formed on the electroforming portion integrally therewith, and is incorporated in the mold portion 14 . Then, the effect of preventing the rotation and the drawing out can be further enhanced.
the flange 20 is formed in an inclined manner on a corner portion of the radial bearing surface A and the thrust bearing surface B, and it is possible to form this type of flange 20 in the electroforming process.
the master shaft 12 of the shown embodiment is immersed into the electrolytic solution, usually, a deposition amount of metal particles is large in a lower end corner portion 12 d of the master shaft 12 as compared with other portions. Accordingly, the inclined flange 20 shown in FIG. 28 grows. Therefore, when the electroforming shaft 11 added with the flanges 20 is formed as it is by the resin material, it becomes possible to use the flange 20 as a portion for preventing the rotation and the drawing out.
the flange 20 can also be formed by plastically deforming the electroforming portion 10 .
a forming position of the flange 20 is not particularly limited, and for example, the flange 20 may also be formed by plastically deforming the upper end of the electroforming portion 10 to the outer diameter side.
FIG. 29 shows a state where the shaft member 2 is drawn out from the bearing member 8 , where an example of the above-mentioned asymmetric forming is shown.
FIG. 29 shows a state where the shaft member 2 is drawn out from the bearing member 8 , where an example of the above-mentioned asymmetric forming is shown.
the dynamic pressure groove 8 a 1 is formed asymmetrically in the radial direction with respect to an axial center thereof (axial center of the region between the upper and lower inclined grooves) by the upper radial bearing portion R 1 , and an axial dimension X 1 of an upper region of the dynamic pressure groove 8 a 1 from the axial center m is set larger than an axial dimension X 2 of a lower region thereof.
the dynamic pressure groove 8 a 2 is formed symmetrically in the axial direction, and axial dimensions of upper and lower regions thereof are individually equal to the above-mentioned axial dimension X 2 .
the feeding force (pumping force) of the lubricating oil by the dynamic pressure grooves when the shaft member 2 is rotated is relatively larger in the upper dynamic pressure groove 8 a 1 than in the lower symmetric dynamic pressure groove 8 a 2 . Therefore, a downward flow of the lubricating oil is generated in the radial bearing gap, thus making it possible to supply the lubricating oil abundantly to the thrust bearing portion T.
the above description illustrates the case of forming the radial bearing surfaces A and the thrust bearing surface B on the electroforming portion 10 formed as a single member.
a construction can also be adopted, in which the electroforming portion 10 is divided into two or more portions, and both of the bearing surfaces A and B are individually formed on electroforming portions thus formed separately.
FIG. 26 shows a construction example of the spindle motor for the information apparatus.
the spindle motor is the one to be used for the disk drive device such as the HDD, and includes the fluid dynamic bearing device 1 which rotatably supports the shaft member 2 in a non-contact fashion, a rotor (disk hub) 3 attached to the shaft member 2 , and a stator coil 4 and a rotor magnet 5 , both of which are opposed to each other through an intermediation of a radial gap.
the stator coil 4 is attached to an outer circumference of a bracket 6
the rotor magnet 5 is attached to an inner circumference of the disk hub 3 .
the bearing member 8 of the fluid dynamic bearing device 1 is attached to an inner circumference of the bracket 6 .
the disk hub 3 On the disk hub 3 , one or a plurality of disks D such as the magnetic disks are held.
the stator coil 4 When the stator coil 4 is energized, the rotor magnet 5 is rotated by electromagnetic force between the stator coil 4 and the rotor magnet 5 , and the disk hub 3 and the shaft member 2 are thereby rotated integrally with each other.
the construction of the present invention can be used not only for the above-mentioned fluid dynamic bearing device 1 but also preferably for fluid dynamic bearing devices with a form shown below.
a description will be made below of the construction of the fluid dynamic bearing device with reference to the drawings. Common reference symbols will be assigned to members having the same constructions as and common functions to those of the fluid dynamic bearing device 1 shown in FIG. 27 , and a repeated description will be omitted.
FIG. 30 is a view showing another embodiment of the fluid dynamic bearing device 1 .
the dynamic pressure grooves 8 a 1 and 8 a 1 serving as the dynamic pressure generating portions are formed on the outer circumferential surface 2 a of the shaft member 2 and the lower end surface 2 b of the shaft member 2 (the dynamic pressure groove formed on the lower end surface 2 b is not shown), and the radial bearing surfaces A and the thrust bearing surface B of the bearing member 8 are formed into a perfect circular shape in cross section and a flat surface shape, respectively, both of which do not have the dynamic pressure grooves.
the outer circumferential surface 12 a and lower end surface 12 c of the master shaft 12 are formed into a perfect circular shape and a flat surface shape in cross section, respectively, both of which do not have the dynamic pressure grooves.
the above-mentioned electroforming process and the molding step are performed using the master shaft 12 .
the master shaft 12 is separated from the shaft bearing member 8 to form the radial bearing surfaces A and the thrust bearing surface B.
the shaft member 2 which is a member different from the master shaft 12 , is inserted into the inner circumference of the bearing member 8 .
the dynamic pressure grooves are preliminarily formed on the outer circumferential surface 2 a and the lower end surface 2 b of the shaft member 2 by means of a mechanical process or etching.
FIG. 31 is a view showing still another embodiment of the fluid dynamic bearing device 1 .
the thrust bearing portion T is composed of a pivot bearing, and each of the radial bearing portions R 1 and R 2 is composed of a perfect circular bearing which does not have the dynamic pressure generating portion.
a convex spherical surface 2 c is formed, and the spherical surface 2 c is supported by the thrust bearing surface portion B with the flat surface shape in a contact fashion therewith, and the thrust bearing portion T composed of the pivot bearing is thus constructed.
the outer circumferential surface 2 a of the shaft member 2 has the perfect circular shape in cross section, which does not have the dynamic pressure grooves, and the perfect circular bearings are composed of the outer circumferential surface 2 a and the radial bearing surfaces A with the perfect circular shape in cross section.
any one of the radial bearing portions R 1 and R 2 and the thrust bearing portion T can also be replaced by the dynamic bearing shown in FIG. 27 or 29 .
the master shaft 12 itself can also be used, as well as a member separate from the master shaft 12 as in the embodiments shown in FIGS. 27 and 29 .
the thrust bearing surface forming portion N 2 with the flat surface shape, which forms the thrust bearing surface B is formed on one end (upper end in FIG. 32 ) of the master shaft 12
the bearing constructing portion 2 c with the convex spherical shape, which constructs the thrust bearing portion T is formed on the other end of the master shaft 12 .
the electroforming portion 10 is formed on the thrust bearing surface forming portion N 2 of the master shaft 12 shown in FIG.
the masking is applied to the bearing constructing portion 2 c , thereby forming the electroforming shaft 11 .
the electroforming shaft 11 is subjected to the insert molding, and the bearing shaft member 8 and the master shaft 12 are separated from each other.
the master shaft 12 is reversed, and the spherical surface 2 c serving as the bearing constructing portion is inserted into the inner circumference of the bearing member 8 , and then the spherical surface 2 c is brought into contact with the thrust bearing surface B.
the thrust bearing portion T composed of the pivot bearing is constructed.
This method is also applied to the embodiments shown in FIG. 27 and FIG. 29 , thus making it possible to directly use the master shaft 12 as the shaft member 2 .
the flat surface is formed on one end surface of the master shaft 12
the dynamic pressure grooves (or a molding mold of the dynamic pressure grooves) is formed on the other end surface.
One of both end surfaces of the master shaft 12 becomes the forming portion of the thrust bearing surface B, and the other becomes a bearing constructing portion for constructing the thrust bearing portion T.
FIGS. 27 and 29 illustrate the constructions of the radial bearing portions R 1 and R 2 for generating a fluid dynamic pressure by the herringbone-shaped and spiral-shaped dynamic pressure grooves.
the present invention is not limited to this, and for example, the multi-lobe bearing and the step bearing, which are shown in FIGS. 17 to 20 , may also be employed as the radial bearing portions R 1 and R 2 .
the perfect circular bearing is fabricated through a step of coating regions of the master shaft 12 , which require the masking, with a masking material 13 (refer to FIG. 34 ), a step of forming the electroforming shaft 11 by performing the electroforming process for an unmasked portion (refer to FIG. 35 ), and a step of forming the bearing member 8 by molding the electroforming portion 10 of the electroforming shaft 11 by a resin and the like (refer to FIG. 5 ), and a step of separating the electroforming portion 10 and the master shaft 12 from each other.
the minimum clearance ⁇ r is represented by a difference r 1 ⁇ r 2 between a radius r 1 of a virtual circle P 1 inscribed to the bearing surface 10 a of the electroforming portion 10 and a radius r 2 of a virtual circle P 2 circumscribed to the outer circumferential surface 2 a of the shaft member 2 . It is desirable that the minimum clearance ⁇ r be set as: ⁇ r ⁇ 0 in a state where the shaft member 2 is inserted into the inner circumference of the bearing member 8 as shown in FIG. 36 .
the size of the minimum clearance ⁇ r mainly depends on the diameter expansion amount of the electroforming portion 10 in the separation step. Accordingly, the thickness and electroforming conditions of the electroforming portion 10 are set so as to obtain such the numeric value as described above for the minimum clearance ⁇ r.
between the inscribed and circumscribed circles P 2 and P 4 of the outer circumferential surface 2 a in FIG. 36 ) of the outer circumferential surface 2 a of the shaft member 2 is set to 4 ⁇ m or less.
the sum of the circularity of the bearing surface 10 a and the circularity of the outer circumferential surface 2 a of the shaft member 2 , which is opposite thereto, is restricted to be 4 ⁇ m or less, and thus the bearing gap between both of the surfaces 10 a and 2 a becomes more even with smaller variations over the circumferential direction.
both of the surfaces 10 a and 2 a can be formed into relatively smooth surfaces, thus making it possible to restrict the abrasion thereof as much as possible when the shaft member 2 and the bearing member 8 rotates relatively to each other.
the outer circumferential surface of the master shaft 12 is subjected to a finishing process so as to satisfy the above-mentioned numerical conditions ( ⁇ r ⁇ 0,
a master shaft with a shaft diameter ⁇ of 1.5 mm and a circularity of 0.5 ⁇ m was fabricated of stainless steel (SUS420F), and the electroforming process was performed therefor for two hours by a sulfamic acid nickel-bath, thereby forming the electroforming portion 10 with a thickness of 0.1 mm. Then, it has been found that a bearing device which satisfies the above-mentioned numerical conditions can be obtained.
the radial bearing portions R 1 and R 2 are composed of the dynamic bearings as shown in FIGS. 8 , 9 , and the like, it is desirable that the above-mentioned numerical conditions be satisfied.
the minimum clearance or is represented by a difference between a radius of a virtual circle inscribed to the protruding portions which define and form the dynamic pressure grooves and a radius of a virtual circle circumscribed to the outer circumferential surface 2 a of the shaft member 2 .
the circularity of the bearing surface 10 a is evaluated by an inner circumferential surface of the protruding portions.
the perfect circular bearing can be used not only as a bearing device for rotation but also as a bearing device for sliding, a bearing device for rotation/sliding, and further, a bearing device for swinging, and it is possible to apply the construction of the present invention to all of those varieties of bearing devices.
the “bearing device for rotation” means a device for supporting the relative rotation between the shaft 2 and the bearing member 8
the “bearing device for sliding” means a device for supporting a relative linear motion between the shaft 2 and the bearing member 8
the “bearing for rotation/sliding” means a device which concurrently has functions of the above-mentioned two bearing devices, for supporting both of the rotational motion and the linear motion between the shaft 2 and the bearing member 8 .
the “bearing for swinging” means a bearing for supporting a swinging motion between the shaft 2 and the bearing member 8 .
the bearing device can also be used by supplying the lubricant such as oil to the bearing gap, as well as is used by supplying no oil thereto.
a lateral cross section of the master shaft 12 is basically formed into a circular shape.
a lateral cross section of the master shaft 12 can be formed into an arbitrary shape such as a polygonal shape and a non-perfect circular shape as well as the circular shape.
the lateral cross-sectional shape of the master shaft 12 is basically constant in the axial direction.
a form is sometimes adopted, in which the lateral cross-sectional shape is not constant over the overall axis of the shaft.
the separate member fabricated separately from the master shaft 12 and with accuracy approximate to that of the master shaft 12 is basically used as the shaft member 2 .
the master shaft 7 can be directly used as the shaft member 2 .
the surface accuracy of the bearing surfaces 4 correspond to the accuracy of the outer circumferential surface of the master shaft 7 . Accordingly, a merit can be obtained that a matching work to be performed after that becomes unnecessary.
the lubricating oil has been shown as the lubricating fluid filled in the inside of the fluid dynamic bearing device.
fluid capable of generating the dynamic pressure in each of the bearing gaps for example, gas such as air can also be used as well as magnetic fluid.
FIG. 1 is a perspective view showing a bearing member according to the present invention
FIG. 2A is a perspective view of a master shaft
FIG. 2B is a perspective view showing a state where masking is performed for the master shaft
FIG. 2C is a perspective view showing an electroforming shaft
FIG. 3 is a cross-sectional view of the bearing member immediately after insert molding
FIG. 4 is a cross-sectional view of an injection molding metal mold
FIG. 5 is across-sectional view of the injection molding metal mold
FIG. 6 is a cross-sectional view of the bearing device
FIG. 7 is a cross-sectional view showing an electroforming step
FIG. 8 is a cross-sectional view of the bearing member
FIG. 9 is a cross-sectional view showing an embodiment of a fluid dynamic bearing device
FIG. 10 is across-sectional view showing an example of a spindle motor using the fluid dynamic bearing device of the present invention.
FIG. 11 is a cross-sectional view showing another example of the spindle motor using the fluid dynamic bearing device of the present invention.
FIG. 12 is a cross-sectional view showing another embodiment of the fluid dynamic bearing device
FIG. 13 is a cross-sectional view showing still another embodiment of the fluid dynamic bearing device
FIG. 14 is a cross-sectional view showing another embodiment of the fluid dynamic bearing device.
FIG. 15 is a cross-sectional view showing still another embodiment of the fluid dynamic bearing device.
FIG. 16 is a cross-sectional view showing yet another embodiment of the fluid dynamic bearing device
FIG. 17 is a cross-sectional view showing another embodiment of a radial bearing portion
FIG. 18 is a cross-sectional view showing another embodiment of the radial bearing portion
FIG. 19 is a cross-sectional view showing still another embodiment of the radial bearing portion
FIG. 20 is a cross-sectional view showing yet another embodiment of the radial bearing portion
FIG. 21 is a perspective view of a bearing member according to the present invention.
FIG. 22A is a perspective view of a master shaft
FIG. 22B is a perspective view showing a state where masking is performed for the master shaft
FIG. 22C is a perspective view showing an electroforming shaft
FIG. 23 is a plan view showing a shaft end of the master shaft
FIG. 24 is a cross-sectional view of the bearing member immediately after insert molding
FIG. 25 is a cross-sectional view showing a molding step
FIG. 26 is a cross-sectional view showing an example of the spindle motor using the fluid dynamic bearing device of the present invention.
FIG. 27 is a cross-sectional view showing an embodiment of the fluid dynamic bearing device
FIG. 28 is a partially enlarged cross-sectional view of the bearing member
FIG. 29 is a cross-sectional view of the bearing member
FIG. 30 is a cross-sectional view showing another embodiment of the fluid dynamic bearing device.
FIG. 31 is a cross-sectional view showing another embodiment of the fluid dynamic bearing device.
FIG. 32 is a front view of a master shaft to be used as a shaft member
FIG. 33 is a perspective view of the mater shaft
FIG. 34 is a perspective view showing the master shaft which is subjected to the masking
FIG. 35 is a perspective view of an electroforming shaft
FIG. 36 is a cross-sectional view of the bearing device in a radius direction, and an enlarged view of the bearing device.

Landscapes

Engineering & Computer Science (AREA)
General Engineering & Computer Science (AREA)
Mechanical Engineering (AREA)
Physics & Mathematics (AREA)
Fluid Mechanics (AREA)
Chemical & Material Sciences (AREA)
Oil, Petroleum & Natural Gas (AREA)
Sliding-Contact Bearings (AREA)
Moulds For Moulding Plastics Or The Like (AREA)

US11/795,410 2005-05-18 2006-05-15 Fluid Dynamic Bearing Device Abandoned US20080212908A1 (en)

Applications Claiming Priority (13)

Application Number	Priority Date	Filing Date	Title
JP2005145517A JP4987248B2 (ja)	2005-05-18	2005-05-18	軸受装置、および該軸受装置を有するモータ
JP2005-145521		2005-05-18
JP2005145373A JP4896428B2 (ja)	2005-05-18	2005-05-18	流体軸受装置およびこれを有するモータ
JP2005145506A JP4896429B2 (ja)	2005-05-18	2005-05-18	軸受、軸受装置、モータ、および軸受の製造方法
JP2005-145373		2005-05-18
JP2005145370A JP2006322502A (ja)	2005-05-18	2005-05-18	軸受部材およびその製造方法
JP2005145362A JP2006322500A (ja)	2005-05-18	2005-05-18	軸受装置
JP2005145521A JP4896430B2 (ja)	2005-05-18	2005-05-18	軸受装置および軸受装置を用いたモータ
JP2005-145517		2005-05-18
JP2005-145370		2005-05-18
JP2005-145506		2005-05-18
JP2005-145362		2005-05-18
PCT/JP2006/309640 WO2006123602A1 (ja)	2005-05-18	2006-05-15	動圧軸受装置

Related Parent Applications (1)

Application Number	Title	Priority Date	Filing Date
PCT/JP2006/309640 A-371-Of-International WO2006123602A1 (ja)	2005-05-18	2006-05-15	動圧軸受装置

Related Child Applications (1)

Application Number	Title	Priority Date	Filing Date
US13/435,915 Division US8931175B2 (en)	2005-05-18	2012-03-30	Fluid dynamic bearing device

Publications (1)

Publication Number	Publication Date
US20080212908A1 true US20080212908A1 (en)	2008-09-04

Family

ID=37431175

Family Applications (2)

Application Number	Title	Priority Date	Filing Date
US11/795,410 Abandoned US20080212908A1 (en)	2005-05-18	2006-05-15	Fluid Dynamic Bearing Device
US13/435,915 Expired - Fee Related US8931175B2 (en)	2005-05-18	2012-03-30	Fluid dynamic bearing device

Family Applications After (1)

Application Number	Title	Priority Date	Filing Date
US13/435,915 Expired - Fee Related US8931175B2 (en)	2005-05-18	2012-03-30	Fluid dynamic bearing device

Country Status (3)

Country	Link
US (2)	US20080212908A1 (ko)
KR (1)	KR101414110B1 (ko)
WO (1)	WO2006123602A1 (ko)

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Also Published As

Publication number	Publication date
KR20080020590A (ko)	2008-03-05
US20120186983A1 (en)	2012-07-26
US8931175B2 (en)	2015-01-13
KR101414110B1 (ko)	2014-07-01
WO2006123602A1 (ja)	2006-11-23

Publication	Publication Date	Title
US8931175B2 (en)	2015-01-13	Fluid dynamic bearing device
US8876388B2 (en)	2014-11-04	Fluid dynamic bearing device
US8562219B2 (en)	2013-10-22	Fluid dynamic bearing device
US7687951B2 (en)	2010-03-30	Fluid dynamic bearing device and motor equipped with the same
CN101203685B (zh)	2012-06-06	流体动态轴承装置
CN101395393A (zh)	2009-03-25	流体轴承装置
JP5058516B2 (ja)	2012-10-24	流体軸受装置
JP4794922B2 (ja)	2011-10-19	流体軸受装置およびこれを有するモータ
JP4896430B2 (ja)	2012-03-14	軸受装置および軸受装置を用いたモータ
JP4813211B2 (ja)	2011-11-09	滑り軸受、これを備えたモータ、及び、滑り軸受の製造方法
JP4896429B2 (ja)	2012-03-14	軸受、軸受装置、モータ、および軸受の製造方法
JP4890066B2 (ja)	2012-03-07	動圧軸受装置及びこれを有するファンモータ
JP2006322500A (ja)	2006-11-30	軸受装置
JP4896428B2 (ja)	2012-03-14	流体軸受装置およびこれを有するモータ
JP2006322502A (ja)	2006-11-30	軸受部材およびその製造方法
JP4794966B2 (ja)	2011-10-19	軸受装置、これを備えたモータ、及び軸受装置の製造方法
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Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MORI, NATSUHIKO;YAMASHITA, NOBUYOSHI;SATOJI, FUMINORI;AND OTHERS;REEL/FRAME:020718/0955;SIGNING DATES FROM 20080313 TO 20080318